This invention relates to self-lapping type brake valves as used in the air brake system of railroad trains.
As is known, a self-lapping type of brake valve is utilized by being installed in the air brake system of railroad trains. This controls the pressure in air pipes, such as in control units, brake cylinders, etc., being based on back-and-forth movement of the fluid pressure valve units which continuously move by rotating the self-lapping can at the set rotation angle by the rotating operation of a lever. This kind of self-lapping type brake valve is shown in the "New Electric Train Air Brake Unit Explanation", 9th edition, pp. 301-214 (Nov. 15, 1974, published by Kouyuu Co.). The conventional technique, as explained, below is based on FIG. 5.
The inside of the housing 101, having a space in it, is divided into the following:
a supply chamber 115 connected to the main air reservoir located outside of this Figure, two partition walls 103, a central opening 102 in each wall, a piston 100 having a diaphragm 104, a power chamber 116 connected to the air line, such as control units, brake cylinders, etc. which are outside of this Figure, a diaphragm chamber 106 connected to the delivery chamber 116 through a throttle valve 117 of the partition wall 103 on the side of the piston 100, and an atmospheric pressure chamber 107 opened to the outside atmosphere.
Within each opening 102 of the two partitions 103 and in the opening 141 formed in an outside wall 140 of the housing 101, a bushing 109 is attached, which forms the ports 142, 143, and 144 on the circumference. Further, inside of the bushing 109, a cylindrical supply valve seat member 112 is installed, which is provided with three O-rings 136 fixed on the circumference. Bushing 109 has a stop ring 110, against which an end cap 119 of supply valve seat member 112 is engaged. The actuator mechanism 122, which moves back-and-forth by the handle operation that is located outside of the Figure, acts on the surface 120 of end cap 119. On the circumference of the supply valve seat member 112, a port 146 is formed, which leads the pressurized air of the supply chamber 115 through the port 142 to a spring chamber 145 in the supply valve seat member 112; and further, a port 147 is formed, which connects with the supply valve seat member 112 through the delivery chamber 116 and the port 143. At the inside of the supply valve seat member 112, a supply valve seat 114 is formed; and the head 127a of the supply valve 127, fitting into the supply valve seat, is placed in a spring chamber 145 in such a way that its foot 127b protrudes from the end of member 112 opposite end cap 119. The supply valve 127 is urged in the direction that holds the supply valve against seat 114 by the supply valve spring 126, which is installed in the spring chamber 145. Further, in case the supply valve 127 comes off of its seat, a passage 148 leads pressurized air (coming from the supply chamber 115) from the spring chamber 145 to the delivery chamber 116 at the foot 127b.
A movable exhaust valve seat 133, which protrudes into the delivery chamber 116 of the piston 100, has a stop that is engageable with bushing 109 of the side adjacent piston 100. Simultaneously, the head 150a of the exhaust valve 150, which is contained in a bore 149 beyond the exhaust valve seat 133, makes contact with the foot 127b of the supply valve 127. Then, the exhaust valve spring 151, supported by a spring seat 134 which is fixed to the piston 100, is connected to the foot 150b of the exhaust valve 150. It always pushes the exhaust valve 150 in the direction of the supply valve 127. The exhaust valve spring 151 is weaker than the supply valve spring 126 when the force of the supply valve spring 126 is conveyed to the exhaust valve 150 via the supply valve 127, due to the resilience of this supply valve spring 126. The piston 100 is always pushed toward the supply valve 127 by the adjusting spring 131, which is installed in the atmospheric pressure chamber 107. Its movement toward the supply valve 127 is limited by engagement with bushing 109. In case the exhaust valve 150 becomes disengaged from the exhaust valve seat 133, a passage 152, which communicates delivery chamber 116 and the atmospheric pressure chamber 107, is opened. In FIG. 5, a spring seat 135 receives the adjusting spring 131, and an adjusting screw 136 adjusts the degree of compression of this adjusting spring 131.
First, the operation that supplies the pneumatic pressure to the delivery chamber 116 is explained.
As the actuator mechanism 122 is operated in the direction of arrow I, the end cap 119 contacted by the actuator mechanism 122, the supply valve seat spool 112, and the supply valve 127 move in the same direction. Thus, the flow path between the delivery chamber 116 and the atmospheric pressure chamber 107 is closed, since the exhaust valve 150 connected to the foot 127b of the supply valve 127 is seated in the exhaust valve seat 133 by overcoming the force of exhaust valve spring 151.
When the actuator mechanism 122 moves in the direction of arrow I, the supply valve 127 is prevented from further moving in the arrow I direction, since the exhaust valve 150 now sits in the exhaust valve seat 133 and is pushed in the direction to the supply valve 127 by the adjusting spring 131. However, the supply valve seat member 112 continues to move, the supply valve spring 126 is compressed, and the supply valve seat 114 becomes free from the supply valve 127. As a result, the pressurized air of the supply chamber 115 is led through the spring chamber 145 to the delivery chamber 116, from where it is led to the diaphragm chamber 106 through throttle 117. The piston 100, which is holding the diaphragm 104, moves against the force of the adjusting spring 131 while the exhaust valve 150 is sitting in the exhaust valve seat 133 until balance between the pressure in the delivery chamber 116 and the resilience of the adjusting spring 131 is established. With this movement, the supply valve 127, which is pushed against the exhaust valve 150 by the supply valve spring 126, moves in the same direction as the exhaust valve 150. Thus, the distance between the supply valve 127 and the supply valve seat 114 gradually becomes shortened until in the end, the supply valve 127 returns to the supply valve seat 114. This then shuts OFF the supply of pressurized air from the supply chamber 115 to the delivery chamber 116, and results in a lap condition in the pressure-buildup phase of brake control.
Now, the releasing operation, that is, the movement that exhausts the pressurized air from the delivery chamber 116, is explained.
When the actuator mechanism 122 is operated in the opposite direction, that is, in the direction of arrow 0, spring 126 becomes caged and thus ineffective to exert resistance to movement of supply valve 127. Accordingly, spring 151 is effective to unseat exhaust valve 150, thereby allowing pressure in diaphragm chamber 106 to exhaust via throttle 117, delivery chamber 116, port 144, the exhaust valve seat 133, and atmospheric chamber 107. At the same time, supply valve 127 remains seated so that no further pressure is supplied while the delivery chamber pressure is being reduced. As the pressure in delivery chamber 116 and diphragm chamber 106 is lowered, piston 100 is moved in the direction of the arrow 0 by the force of the adjusting spring 131 along with the exhaust valve seat 133. With this, the distance between the exhaust valve 150 and the exhaust valve seat 133 becomes shortened. At last, the exhaust valve seat 133 shuts OFF the exhaust to the atmospheric pressure chamber 107 from the delivery chamber 116 by engagement with the exhaust valve 150, and results in a lap condition in the pressure-release phase of brake control.
In the foregoing, the explanation covers the situation in which the delivery chamber pressure is used for a straight air brake. When it is desired to utilize the delivery chamber pressure for controlling an automatic brake, the above-explained brake movement and brake-release movement become just opposite. Therefore, a detailed explanation is omitted here.
According to the conventional technique, the following relationship is established: the force in the lap condition during a pressure-buildup, which balances the resilience W.sub.1 ' of the adjusting spring 131 that acts on the piston 100 and attached diaphragm 104, is equal to the force which the pressure PA of the supply chamber 115 exerts on the supply valve 127, plus the difference of the force that the pressure PB of the delivery chamber 116 exerts on the effective area A.sub.1 ' of the piston 100 and the force that the pressure PB of the delivery chamber 116 exerts on the supply valve 127, namely, on the effective area A.sub.2 ' of the supply valve seat 114. Thus, the following equation is established: EQU (A.sub.1 '-A.sub.2 ').times.PB+A.sub.2 '.times.PA=W.sub.1 '(a)
On the other hand, in the lap condition during pressure-release, the force A.sub.2 '.times.PA in the above equation (a), which acts on the supply valve 127 is supported by the supply valve seat 114 and is not transmitted to spring 131. Thus, the following equation is possible: EQU (A.sub.1 '-A.sub.2).times.PB=W.sub.1' (b)
As is clear from equations (a) and (b), the force against W.sub.1 ' during pressure-buildup lap time is different from the force during pressure-release lap time. This is hysteresis, that is, the pressure PB of the delivery chamber 116 is different when applying the brake and when releasing the brake, even though the setting of actuator mechanism 122 is the same. Thus, the fact that the control effect of the railroad train differs, becomes a problem.
The cause of this problem is that the force A.sub.2 '.times.PA in the above equation (a) exists.